At a location near the driver's seat, there are provided manual switches and an auto switch as switches for the power window.
When the auto switch is operated by the driver so that the contacts for raising operation or the contacts for lowering operation are brought into the ON state, the drive of the motor is continued until the door glass is completely closed or completely opened even after the driver releases the auto switch. When the door glass is completely closed, the movement of the door glass is prevented by the widow frame or the like, whereby the drive current of the motor increases. The drive of the motor is stopped when the drive current exceeds a predetermined level.
By the way, it has been considered to detect an abnormal current due to the existence of a foreign object on the locus of the upward movement of the door glass so as to stop or reverse the motor. In some systems, there is provided a full-closure detecting switch for detecting the state that the door glass approaches its full closure position so as to discriminate a current increase due to the foreign object from a current increase due to the full closure of the door glass.
However, in the case where the detected drive current of the motor exceeds the predetermined value due to rush current at the beginning of the drive of the motor, such an increase in the drive current is sometimes regarded as abnormal current. To overcome this problem, a blanking period is provided for stopping the comparison between the variation amount of the motor current and the predetermined value at the beginning of the drive of the motor, thereby preventing unnecessary operations due to the above-described rush current.
However, the above-described conventional art has a problem that the catching of a foreign object cannot be detected if such catching occurs in a predetermined period of time (blanking period) following the start of the motor. If the blanking period is shortened considerably, a possibility arises that the variation amount of the motor current exceeds the predetermined value due to a variation in current (especially, an increase in current) which occurs during the transient period after the flow of rush current has started.